Ion implantation is a physical process that is employed in semiconductor device fabrication to selectively implant dopant into semiconductor and/or wafer material. Thus, the act of implanting does not rely on a chemical interaction between a dopant and semiconductor material. For ion implantation, dopant atoms/molecules are ionized, accelerated, formed into a beam, analyzed, and swept across a wafer, or the wafer is swept through the beam. The dopant ions physically bombard the wafer, enter the surface and come to rest below the surface, at a depth related to their energy.
An ion implantation system is a collection of sophisticated subsystems, each performing a specific action on the dopant ions. In one example, dopant elements, in gas or solid form, are introduced inside an ionization chamber and ionized by a suitable ionization process. In one example process, the chamber is maintained at a low pressure (vacuum). A filament or indirectly heated cathode is located within the chamber and is heated to the point where electrons are created from the cathode source. The negatively charged electrons are attracted to an oppositely charged anode also within the chamber. During the travel from the cathode to the anode, the electrons collide with the dopant source elements (e.g., molecules or atoms) and create a host of positively charged ions from the source gas material.
Generally, other positive ions are created in addition to desired dopant ions. The desired dopant ions are selected from the ions by a process referred to as analyzing, mass analyzing, selection, or ion separation. Selection is accomplished utilizing a mass analyzer that creates a magnetic field through which ions from the ionization chamber travel. The ions leave the ionization chamber at relatively high speeds and are bent into an arc by the magnetic field. The radius of the arc is dictated by the mass of individual ions, speed, and the strength of the magnetic field. An exit of the analyzer permits only one species of ions, the desired dopant ions, to exit the mass analyzer.
An acceleration system is employed to accelerate or decelerate the desired dopant ions to a predetermined momentum (e.g., mass of a dopant ion multiplied by its velocity) to penetrate the wafer surface. For acceleration, the system is generally of a linear design with annular powered electrodes along its axis. As the dopant ions enter therein, they are accelerated there through.
Subsequently, the accelerated ions within the beam are directed toward a target wafer or location. The ion beam strikes the target with an actual angle of incidence, which is typically measured in one or two dimensions from normal. This actual angle can vary from a desired or selected angle of implantation.
Operation of an ion implantation system or other ion beam equipment (e.g., linear accelerators) may result in the production of contaminant particles. These particles can result in a number of ways, such as ions striking photoresist coated surfaces, particles breaking off of components within the system, and the like. The contaminant particles can interfere with ion implantation processes and degrade and/or destroy semiconductor devices undergoing ion implantation. For example, particles can collide with and adhere to target wafers during ion implantation resulting in yield loss. As another example, the particles can become implanted impacting device operation.
As a result, semiconductor device manufactures may measure particles on semiconductor wafers after ion implantation. This measurement allows a determination or estimation of particles present within an ion beam during ion implantation. However, only a small fraction of the particles are measured and adjustments can only be performed after the ion implantation process has concluded.